1. Field of the Invention
This invention relates to a novel emulsifying composition of a water-in-oil type.
2. Description of the Prior Art
As is generally known, emulsions of a water-in-oil (W/O) type consisting of water dispersed in an oil phase possess a higher antibacterial activity than those of an oil-in-water (O/W) type in which the phases are reversed. Another advantage of the W/O emulsions is easy retention of water in the emulsions. Because of these substantial advantages, the W/O emulsions have found application to cosmetics and further to oils for use in textile finishing, metal processing and similar treatment.
However, the known W/O emulsions suffer from some defects whereby the use of such emulsions is currently being restricted as compared to O/W emulsions.
In general, the breaking of emulsions is due to aggregation of particles with subsequent coalescence of the aggregates. Since the rate of aggregation is greater than that of coalescence, it is necessary to prevent aggregation at an initial stage in order to prevent breaking of the emulsions. In the O/W emulsions where water is the dispersion medium or continuous liquid, water is separated from an aggregated phase. However, the water thus separated, if in small quantities, does not exert any adverse effects upon the properties of the O/W emulsions because it is so volatile as to be substantially removed from the emulsions. In contrast to the O/W emulsions, the separation of oil takes place as a consequence of aggregation in the W/0 emulsions in which oil is the disperse liquid or continuous phase. The oil once separated, even if in small quantities, is not readily volatile but becomes virtually present in the emulsions. This is particularly detrimental to the appearance or commercial acceptance of the W/O emulsions.
Such defects make it difficult to prepare W/O emulsions which are stable over a wide range of temperatures. Furthermore, the absence of any suitable emulsifying agents creates an obstacle to surmounting these defects.
In view of the disadvantages possessed by the existing W/O emulsions, the present inventors have made intensive studies of a variety of compounds or emulsifying agents which are effective in stabilizing W/O emulsions. From these studies, it has been found that polyoxyethylene sorbitol fatty acid esters of a specific class in combination with multivalent metal salts of fatty acids of a specific class achieve the above desired properties and give the best results.